This invention relates to an improved post hole digger. In particular, the invention is directed to a tractor-mounted, hydraulic thrust, post hole digger having an improved boom construction.
There are various types of known tractor-mounted post hole diggers, and examples can be found in U.S. Pat. Nos. 3,700,045 and 5,507,354. Such post hole diggers typically have an auger rotatably mounted on a frame which is attached to the three-point hitch at the rear of a tractor. The auger may be driven by the tractor""s power take off (PTO).
The post hole digger of U.S. Pat. No. 5,507,354 is an example of a power-assisted drilling apparatus, sometimes known as a xe2x80x9chydraulic thrustxe2x80x9d post hole digger, in which a downward force is applied to an auger as the auger is rotated, in order to provide faster and more efficient penetration of the earth, particularly in hard or rock-laden soils.
The post hole digger of U.S. Pat. No. 5,507,354 has a boom assembly comprising a pair of laterally displaced bipartite booms. Each boom comprises first and second arms welded together with an angle of approximately 45xc2x0 therebetween. The second arm of each boom (i.e. the arm more distant from the tractor) is shorter than the first arm.
Boom assemblies (hereinafter referred to simply as xe2x80x9cboomsxe2x80x9d) which are used in post hole diggers, such as that of U.S. Pat. No. 5,507,354, are typically formed from lengths of steel tubular sections which are cut, positioned and welded to form a desired configuration. The cutting and welding of such sections is a time consuming process which adds to the cost of manufacture, and hence the cost of the finished product.
Moreover, considerable forces may be applied to the booms in use, e.g. when hydraulic thrust drilling in hard or rock-laden soils. Such forces create high stresses at the rigid angled joints of the boom arms, with potential failure of the joints if not constructed properly. Increasing the size of the boom arms to accommodate such stresses increases the overall weight of the post hole digger.
It is an object of this invention to provide an improved boom for a post hole digger which overcomes or at least ameliorates, the abovedescribed disadvantages.
In one form, the invention provides drilling apparatus comprising
a frame suitable for attachment to a three-point hitch at the rear of a tractor,
a boom pivotally connected at its proximal end to the frame, the boom being pivotable relative to the frame about a substantially horizontal pivot axis,
an auger rotatably mounted to the boom at or near the distal end of the boom,
a hydraulic cylinder connected between the boom and the frame, for pivoting the boom relative to the frame to thereby raise or lower the auger,
wherein the boom comprises a pair of boom arms spaced laterally apart and connected by at least one crosspiece located intermediate the ends of each boom arm, each boom arm being an integrally formed angled arm which extends substantially from the proximal end to the distal end of the boom,
and wherein the hydraulic cylinder is connected between the frame and the crosspiece, and is located wholly above the pivot axis.
The term xe2x80x9cangled armxe2x80x9d as used in this specification is intended to include a curved arm, as well as an arm having a curved portion along its length.
Typically, the drilling apparatus is a tractor-mounted post hole digger.
Each angled arm may comprise a first (proximal) straight portion, a second (distal) straight portion and a curved portion between the two straight portions. The distal straight portion is preferably longer than the proximal straight portion.
Each angled arm is typically formed from a length of metal tube shaped by a cold working process, such as bending in a pipe bender.
By forming the boom from unipartite angled arms, the manufacturing costs are substantially reduced. Moreover, the use of unipartite angled arms with curved portions provides mechanical strength and flexing advantages over similarly sized welded constructions, thereby enabling the size of the arms to be reduced for a given strength rating.
In another form, the invention provides a boom for a tractor-mounted post hole digger, the boom comprising a pair of boom arms spaced laterally apart and connected by at least one crosspiece located intermediate the ends of each boom arm, each boom arm being an integrally formed unipartite angled arm extending substantially the whole length of the boom, and wherein each angled arm comprises a proximal straight portion, a distal straight portion, and a curved portion between the proximal and distal portions.
In order that the invention may be more fully understood and put into practice, a preferred embodiment will now be described by way of example, with reference to the accompanying drawings.